Scientists have long been aware of a link between the gut microbiome and the central nervous system (CNS). Until now, however, the immune cells that move from the gut into the CNS and thus the brain had not been identified. A team of researchers in Munich (including SyNergy members Lisa Ann Gerdes, Bernhard Hemmer, Thomas Misgeld, Klaus Dornmair, and Thomas Korn) has now succeeded in using violet light to make these migrating T cells visible for the first time. This opens up avenues for developing new treatment options for diseases such as multiple sclerosis (MS) and cancer.